text: /*
   * The Lean Mean C++ Option Parser
   *
   * Copyright (C) 2012 Matthias S. Benkmann
   *
   * The "Software" in the following 2 paragraphs refers to this file containing
   * the code to The Lean Mean C++ Option Parser.
   * The "Software" does NOT refer to any other files which you
   * may have received alongside this file (e.g. as part of a larger project that
   * incorporates The Lean Mean C++ Option Parser).
   *
   * Permission is hereby granted, free of charge, to any person obtaining a copy
   * of this software, to deal in the Software without restriction, including
   * without limitation the rights to use, copy, modify, merge, publish,
   * distribute, sublicense, and/or sell copies of the Software, and to permit
   * persons to whom the Software is furnished to do so, subject to the following
   * conditions:
   * The above copyright notice and this permission notice shall be included in
   * all copies or substantial portions of the Software.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
   * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
   * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
   * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
   * SOFTWARE.
   */
  
  /*
   * NOTE: It is recommended that you read the processed HTML doxygen documentation
   * rather than this source. If you don't know doxygen, it's like javadoc for C++.
   * If you don't want to install doxygen you can find a copy of the processed
   * documentation at
   *
   * http://optionparser.sourceforge.net/
   *
   */
  
  /**
   * @file
   *
   * @brief This is the only file required to use The Lean Mean C++ Option Parser.
   *        Just \#include it and you're set.
   *
   * The Lean Mean C++ Option Parser handles the program's command line arguments 
   * (argc, argv).
   * It supports the short and long option formats of getopt(), getopt_long() 
   * and getopt_long_only() but has a more convenient interface.
   * The following features set it apart from other option parsers:
   *
   * @par Highlights:
   * <ul style="padding-left:1em;margin-left:0">
  #include "optionparser.hpp"
   * <li> It is freestanding. There are no dependencies whatsoever, not even the
   *      C or C++ standard library.
   * <li> It has a usage message formatter that supports column alignment and
   *      line wrapping. This aids localization because it adapts to
   *      translated strings that are shorter or longer (even if they contain
   *      Asian wide characters).
   * <li> Unlike getopt() and derivatives it doesn't force you to loop through
   *     options sequentially. Instead you can access options directly like this:
   *     <ul style="margin-top:.5em">
   *     <li> Test for presence of a switch in the argument vector:
   *      @code if ( options[QUIET] ) ... @endcode
   *     <li> Evaluate --enable-foo/--disable-foo pair where the last one used wins:
   *     @code if ( options[FOO].last()->type() == DISABLE ) ... @endcode
   *     <li> Cumulative option (-v verbose, -vv more verbose, -vvv even more verbose):
   *     @code int verbosity = options[VERBOSE].count(); @endcode
   *     <li> Iterate over all --file=&lt;fname> arguments:
   *     @code for (Option* opt = options[FILE]; opt; opt = opt->next())
   *   fname = opt->arg; ... @endcode
   *     <li> If you really want to, you can still process all arguments in order:
   *     @code
   *   for (int i = 0; i < p.optionsCount(); ++i) {
   *     Option& opt = buffer[i];
   *     switch(opt.index()) {
   *       case HELP:    ...
   *       case VERBOSE: ...
   *       case FILE:    fname = opt.arg; ...
   *       case UNKNOWN: ...
   *     @endcode
   *     </ul>
   * </ul> @n
   * Despite these features the code size remains tiny. 
   * It is smaller than <a href="http://uclibc.org">uClibc</a>'s GNU getopt() and just a
   * couple 100 bytes larger than uClibc's SUSv3 getopt(). @n
   * (This does not include the usage formatter, of course. But you don't have to use that.)
   *
   * @par Download:
   * Tarball with examples and test programs:
   * <a style="font-size:larger;font-weight:bold" href="http://sourceforge.net/projects/optionparser/files/optionparser-1.3.tar.gz/download">optionparser-1.3.tar.gz</a> @n
   * Just the header (this is all you really need):
   * <a style="font-size:larger;font-weight:bold" href="http://optionparser.sourceforge.net/optionparser.h">optionparser.h</a>
   *
   * @par Changelog:
   * <b>Version 1.3:</b> Compatible with Microsoft Visual C++. @n
   * <b>Version 1.2:</b> Added @ref option::Option::namelen "Option::namelen" and removed the extraction
   *                     of short option characters into a special buffer. @n
   *                     Changed @ref option::Arg::Optional "Arg::Optional" to accept arguments if they are attached
   *                     rather than separate. This is what GNU getopt() does and how POSIX recommends
   *                     utilities should interpret their arguments.@n
   * <b>Version 1.1:</b> Optional mode with argument reordering as done by GNU getopt(), so that
   *                     options and non-options can be mixed. See
   *                     @ref option::Parser::parse() "Parser::parse()".
   *
   * @par Feedback:
   * Send questions, bug reports, feature requests etc. to: <tt><b>optionparser-feedback<span id="antispam">&nbsp;(a)&nbsp;</span>lists.sourceforge.net</b></tt>
   * @htmlonly <script type="text/javascript">document.getElementById("antispam").innerHTML="@"</script> @endhtmlonly
   *
   *
   * @par Example program:
   * (Note: @c option::* identifiers are links that take you to their documentation.)
   * @code
   * #include <iostream>
  #include "optionparser.hpp"
   *
   * enum  optionIndex { UNKNOWN, HELP, PLUS };
   * const option::Descriptor usage[] =
   * {
   *  {UNKNOWN, 0,"" , ""    ,option::Arg::None, "USAGE: example [options]\n\n"
   *                                             "Options:" },
   *  {HELP,    0,"" , "help",option::Arg::None, "  --help  \tPrint usage and exit." },
   *  {PLUS,    0,"p", "plus",option::Arg::None, "  --plus, -p  \tIncrement count." },
   *  {UNKNOWN, 0,"" ,  ""   ,option::Arg::None, "\nExamples:\n"
   *                                             "  example --unknown -- --this_is_no_option\n"
   *                                             "  example -unk --plus -ppp file1 file2\n" },
   *  {0,0,0,0,0,0}
   * };
   *
   * int main(int argc, char* argv[])
   * {
   *   argc-=(argc>0); argv+=(argc>0); // skip program name argv[0] if present
   *   option::Stats  stats(usage, argc, argv);
   *   option::Option options[stats.options_max], buffer[stats.buffer_max];
   *   option::Parser parse(usage, argc, argv, options, buffer);
   *
   *   if (parse.error())
   *     return 1;
   *
   *   if (options[HELP] || argc == 0) {
   *     option::printUsage(std::cout, usage);
   *     return 0;
   *   }
   *
   *   std::cout << "--plus count: " <<
   *     options[PLUS].count() << "\n";
   *
   *   for (option::Option* opt = options[UNKNOWN]; opt; opt = opt->next())
   *     std::cout << "Unknown option: " << opt->name << "\n";
   *
   *   for (int i = 0; i < parse.nonOptionsCount(); ++i)
   *     std::cout << "Non-option #" << i << ": " << parse.nonOption(i) << "\n";
   * }
   * @endcode
   *
   * @par Option syntax:
   * @li The Lean Mean C++ Option Parser follows POSIX <code>getopt()</code> conventions and supports
   *     GNU-style <code>getopt_long()</code> long options as well as Perl-style single-minus
   *     long options (<code>getopt_long_only()</code>).
   * @li short options have the format @c -X where @c X is any character that fits in a char.
   * @li short options can be grouped, i.e. <code>-X -Y</code> is equivalent to @c -XY.
   * @li a short option may take an argument either separate (<code>-X foo</code>) or
   *     attached (@c -Xfoo). You can make the parser accept the additional format @c -X=foo by
   *     registering @c X as a long option (in addition to being a short option) and
   *     enabling single-minus long options.
   * @li an argument-taking short option may be grouped if it is the last in the group, e.g.
   *     @c -ABCXfoo or <code> -ABCX foo </code> (@c foo is the argument to the @c -X option).
   * @li a lone minus character @c '-' is not treated as an option. It is customarily used where
   *     a file name is expected to refer to stdin or stdout.
   * @li long options have the format @c --option-name.
   * @li the option-name of a long option can be anything and include any characters.
   *     Even @c = characters will work, but don't do that.
   * @li [optional] long options may be abbreviated as long as the abbreviation is unambiguous.
   *     You can set a minimum length for abbreviations.
   * @li [optional] long options may begin with a single minus. The double minus form is always
   *     accepted, too.
   * @li a long option may take an argument either separate (<code> --option arg </code>) or
   *     attached (<code> --option=arg </code>). In the attached form the equals sign is mandatory.
   * @li an empty string can be passed as an attached long option argument: <code> --option-name= </code>.
   *     Note the distinction between an empty string as argument and no argument at all.
   * @li an empty string is permitted as separate argument to both long and short options.
   * @li Arguments to both short and long options may start with a @c '-' character. E.g.
   *     <code> -X-X </code>, <code>-X -X</code> or <code> --long-X=-X </code>. If @c -X
   *     and @c --long-X take an argument, that argument will be @c "-X" in all 3 cases.
   * @li If using the built-in @ref option::Arg::Optional "Arg::Optional", optional arguments must
   *     be attached.
   * @li the special option @c -- (i.e. without a name) terminates the list of
   *     options. Everything that follows is a non-option argument, even if it starts with
   *     a @c '-' character. The @c -- itself will not appear in the parse results.
   * @li the first argument that doesn't start with @c '-' or @c '--' and does not belong to
   *     a preceding argument-taking option, will terminate the option list and is the
   *     first non-option argument. All following command line arguments are treated as
   *     non-option arguments, even if they start with @c '-' . @n
   *     NOTE: This behaviour is mandated by POSIX, but GNU getopt() only honours this if it is
   *     explicitly requested (e.g. by setting POSIXLY_CORRECT). @n
   *     You can enable the GNU behaviour by passing @c true as first argument to
   *     e.g. @ref option::Parser::parse() "Parser::parse()".
   * @li Arguments that look like options (i.e. @c '-' followed by at least 1 character) but
   *     aren't, are NOT treated as non-option arguments. They are treated as unknown options and
   *     are collected into a list of unknown options for error reporting. @n
   *     This means that in order to pass a first non-option
   *     argument beginning with the minus character it is required to use the
   *     @c -- special option, e.g.
   *     @code
   *     program -x -- --strange-filename
   *     @endcode
   *     In this example, @c --strange-filename is a non-option argument. If the @c --
   *     were omitted, it would be treated as an unknown option. @n
   *     See @ref option::Descriptor::longopt for information on how to collect unknown options.
   *
   */
  
  #ifndef OPTIONPARSER_H_
  #define OPTIONPARSER_H_
  
  /** @brief The namespace of The Lean Mean C++ Option Parser. */
  namespace OptionParser {
  
  #ifdef _MSC_VER
  #include <intrin.h>
  #pragma intrinsic(_BitScanReverse)
  struct MSC_Builtin_CLZ
  {
    static int builtin_clz(unsigned x)
    {
      unsigned long index;
      _BitScanReverse(&index, x);
      return 32-index; // int is always 32bit on Windows, even for target x64
    }
  };
  #define __builtin_clz(x) MSC_Builtin_CLZ::builtin_clz(x)
  #endif
  
  class Option;
  
  /**
   * @brief Possible results when checking if an argument is valid for a certain option.
   *
   * In the case that no argument is provided for an option that takes an
   * optional argument, return codes @c ARG_OK and @c ARG_IGNORE are equivalent.
   */
  enum ArgStatus
  {
    //! The option does not take an argument.
    ARG_NONE,
    //! The argument is acceptable for the option.
    ARG_OK,
    //! The argument is not acceptable but that's non-fatal because the option's argument is optional.
    ARG_IGNORE,
    //! The argument is not acceptable and that's fatal.
    ARG_ILLEGAL
  };
  
  /**
   * @brief Signature of functions that check if an argument is valid for a certain type of option.
   *
   * Every Option has such a function assigned in its Descriptor.
   * @code
   * Descriptor usage[] = { {UNKNOWN, 0, "", "", Arg::None, ""}, ... };
   * @endcode
   *
   * A CheckArg function has the following signature:
   * @code ArgStatus CheckArg(const Option& option, bool msg); @endcode
   *
   * It is used to check if a potential argument would be acceptable for the option.
   * It will even be called if there is no argument. In that case @c option.arg will be @c NULL.
   *
   * If @c msg is @c true and the function determines that an argument is not acceptable and
   * that this is a fatal error, it should output a message to the user before
   * returning @ref ARG_ILLEGAL. If @c msg is @c false the function should remain silent (or you
   * will get duplicate messages).
   *
   * See @ref ArgStatus for the meaning of the return values.
   *
   * While you can provide your own functions,
   * often the following pre-defined checks (which never return @ref ARG_ILLEGAL) will suffice:
   *
   * @li @c Arg::None @copybrief Arg::None
   * @li @c Arg::Optional @copybrief Arg::Optional
   *
   */
  typedef ArgStatus (*CheckArg)(const Option& option, bool msg);
  
  /**
   * @brief Describes an option, its help text (usage) and how it should be parsed.
   *
   * The main input when constructing an option::Parser is an array of Descriptors.
  
   * @par Example:
   * @code
   * enum OptionIndex {CREATE, ...};
   * enum OptionType {DISABLE, ENABLE, OTHER};
   *
   * const option::Descriptor usage[] = {
   *   { CREATE,                                            // index
   *     OTHER,                                             // type
   *     "c",                                               // shortopt
   *     "create",                                          // longopt
   *     Arg::None,                                         // check_arg
   *     "--create  Tells the program to create something." // help
   *   }
   *   , ...
   * };
   * @endcode
   */
  struct Descriptor
  {
    /**
     * @brief Index of this option's linked list in the array filled in by the parser.
     *
     * Command line options whose Descriptors have the same index will end up in the same
     * linked list in the order in which they appear on the command line. If you have
     * multiple long option aliases that refer to the same option, give their descriptors
     * the same @c index.
     *
     * If you have options that mean exactly opposite things
     * (e.g. @c --enable-foo and @c --disable-foo ), you should also give them the same
     * @c index, but distinguish them through different values for @ref type.
     * That way they end up in the same list and you can just take the last element of the
     * list and use its type. This way you get the usual behaviour where switches later
     * on the command line override earlier ones without having to code it manually.
     *
     * @par Tip:
     * Use an enum rather than plain ints for better readability, as shown in the example
     * at Descriptor.
     */
    const unsigned index;
  
    /**
     * @brief Used to distinguish between options with the same @ref index.
     * See @ref index for details.
     *
     * It is recommended that you use an enum rather than a plain int to make your
     * code more readable.
     */
    const int type;
  
    /**
     * @brief Each char in this string will be accepted as a short option character.
     *
     * The string must not include the minus character @c '-' or you'll get undefined
     * behaviour.
     *
     * If this Descriptor should not have short option characters, use the empty
     * string "". NULL is not permitted here!
     *
     * See @ref longopt for more information.
     */
    const char* const shortopt;
  
    /**
     * @brief The long option name (without the leading @c -- ).
     *
     * If this Descriptor should not have a long option name, use the empty
     * string "". NULL is not permitted here!
     *
     * While @ref shortopt allows multiple short option characters, each
     * Descriptor can have only a single long option name. If you have multiple
     * long option names referring to the same option use separate Descriptors
     * that have the same @ref index and @ref type. You may repeat
     * short option characters in such an alias Descriptor but there's no need to.
     *
     * @par Dummy Descriptors:
     * You can use dummy Descriptors with an
     * empty string for both @ref shortopt and @ref longopt to add text to
     * the usage that is not related to a specific option. See @ref help.
     * The first dummy Descriptor will be used for unknown options (see below).
     *
     * @par Unknown Option Descriptor:
     * The first dummy Descriptor in the list of Descriptors,
     * whose @ref shortopt and @ref longopt are both the empty string, will be used
     * as the Descriptor for unknown options. An unknown option is a string in
     * the argument vector that is not a lone minus @c '-' but starts with a minus
     * character and does not match any Descriptor's @ref shortopt or @ref longopt. @n
     * Note that the dummy descriptor's @ref check_arg function @e will be called and
     * its return value will be evaluated as usual. I.e. if it returns @ref ARG_ILLEGAL
     * the parsing will be aborted with <code>Parser::error()==true</code>. @n
     * if @c check_arg does not return @ref ARG_ILLEGAL the descriptor's
     * @ref index @e will be used to pick the linked list into which
     * to put the unknown option. @n
     * If there is no dummy descriptor, unknown options will be dropped silently.
     *
     */
    const char* const longopt;
  
    /**
     * @brief For each option that matches @ref shortopt or @ref longopt this function
     * will be called to check a potential argument to the option.
     *
     * This function will be called even if there is no potential argument. In that case
     * it will be passed @c NULL as @c arg parameter. Do not confuse this with the empty
     * string.
     *
     * See @ref CheckArg for more information.
     */
    const CheckArg check_arg;
  
    /**
     * @brief The usage text associated with the options in this Descriptor.
     *
     * You can use option::printUsage() to format your usage message based on
     * the @c help texts. You can use dummy Descriptors where
     * @ref shortopt and @ref longopt are both the empty string to add text to
     * the usage that is not related to a specific option.
     *
     * See option::printUsage() for special formatting characters you can use in
     * @c help to get a column layout.
     *
     * @attention
     * Must be UTF-8-encoded. If your compiler supports C++11 you can use the "u8"
     * prefix to make sure string literals are properly encoded.
     */
    const char* help;
  };
  
  /**
   * @brief A parsed option from the command line together with its argument if it has one.
   *
   * The Parser chains all parsed options with the same Descriptor::index together
   * to form a linked list. This allows you to easily implement all of the common ways
   * of handling repeated options and enable/disable pairs.
   *
   * @li Test for presence of a switch in the argument vector:
   *      @code if ( options[QUIET] ) ... @endcode
   * @li Evaluate --enable-foo/--disable-foo pair where the last one used wins:
   *     @code if ( options[FOO].last()->type() == DISABLE ) ... @endcode
   * @li Cumulative option (-v verbose, -vv more verbose, -vvv even more verbose):
   *     @code int verbosity = options[VERBOSE].count(); @endcode
   * @li Iterate over all --file=&lt;fname> arguments:
   *     @code for (Option* opt = options[FILE]; opt; opt = opt->next())
   *   fname = opt->arg; ... @endcode
   */
  class Option
  {
    Option* next_;
    Option* prev_;
  public:
    /**
     * @brief Pointer to this Option's Descriptor.
     *
     * Remember that the first dummy descriptor (see @ref Descriptor::longopt) is used
     * for unknown options.
     *
     * @attention
     * @c desc==NULL signals that this Option is unused. This is the default state of
     * elements in the result array. You don't need to test @c desc explicitly. You
     * can simply write something like this:
     * @code
     * if (options[CREATE])
     * {
     *   ...
     * }
     * @endcode
     * This works because of <code> operator const Option*() </code>.
     */
    const Descriptor* desc;
  
    /**
     * @brief The name of the option as used on the command line.
     *
     * The main purpose of this string is to be presented to the user in messages.
     *
     * In the case of a long option, this is the actual @c argv pointer, i.e. the first
     * character is a '-'. In the case of a short option this points to the option
     * character within the @c argv string.
     *
     * Note that in the case of a short option group or an attached option argument, this
     * string will contain additional characters following the actual name. Use @ref namelen
     * to filter out the actual option name only.
     *
     */
    const char* name;
  
    /**
     * @brief Pointer to this Option's argument (if any).
     *
     * NULL if this option has no argument. Do not confuse this with the empty string which
     * is a valid argument.
     */
    const char* arg;
  
    /**
     * @brief The length of the option @ref name.
     *
     * Because @ref name points into the actual @c argv string, the option name may be
     * followed by more characters (e.g. other short options in the same short option group).
     * This value is the number of bytes (not characters!) that are part of the actual name.
     *
     * For a short option, this length is always 1. For a long option this length is always
     * at least 2 if single minus long options are permitted and at least 3 if they are disabled.
     *
     * @note
     * In the pathological case of a minus within a short option group (e.g. @c -xf-z), this
     * length is incorrect, because this case will be misinterpreted as a long option and the
     * name will therefore extend to the string's 0-terminator or a following '=" character
     * if there is one. This is irrelevant for most uses of @ref name and @c namelen. If you
     * really need to distinguish the case of a long and a short option, compare @ref name to
     * the @c argv pointers. A long option's @c name is always identical to one of them,
     * whereas a short option's is never.
     */
    int namelen;
  
    /**
     * @brief Returns Descriptor::type of this Option's Descriptor, or 0 if this Option
     * is invalid (unused).
     *
     * Because this method (and last(), too) can be used even on unused Options with desc==0, you can (provided
     * you arrange your types properly) switch on type() without testing validity first.
     * @code
     * enum OptionType { UNUSED=0, DISABLED=0, ENABLED=1 };
     * enum OptionIndex { FOO };
     * const Descriptor usage[] = {
     *   { FOO, ENABLED,  "", "enable-foo",  Arg::None, 0 },
     *   { FOO, DISABLED, "", "disable-foo", Arg::None, 0 },
     *   { 0, 0, 0, 0, 0, 0 } };
     * ...
     * switch(options[FOO].last()->type()) // no validity check required!
     * {
     *   case ENABLED: ...
     *   case DISABLED: ...  // UNUSED==DISABLED !
     * }
     * @endcode
     */
    int type() const
    {
      return desc == 0 ? 0 : desc->type;
    }
  
    /**
     * @brief Returns Descriptor::index of this Option's Descriptor, or -1 if this Option
     * is invalid (unused).
     */
    int index() const
    {
      return desc == 0 ? -1 : desc->index;
    }
  
    /**
     * @brief Returns the number of times this Option (or others with the same Descriptor::index)
     * occurs in the argument vector.
     *
     * This corresponds to the number of elements in the linked list this Option is part of.
     * It doesn't matter on which element you call count(). The return value is always the same.
     *
     * Use this to implement cumulative options, such as -v, -vv, -vvv for
     * different verbosity levels.
     *
     * Returns 0 when called for an unused/invalid option.
     */
    int count()
    {
      int c = (desc == 0 ? 0 : 1);
      Option* p = first();
      while (!p->isLast())
      {
        ++c;
        p = p->next_;
      };
      return c;
    }
  
    /**
     * @brief Returns true iff this is the first element of the linked list.
     *
     * The first element in the linked list is the first option on the command line
     * that has the respective Descriptor::index value.
     *
     * Returns true for an unused/invalid option.
     */
    bool isFirst() const
    {
      return isTagged(prev_);
    }
  
    /**
     * @brief Returns true iff this is the last element of the linked list.
     *
     * The last element in the linked list is the last option on the command line
     * that has the respective Descriptor::index value.
     *
     * Returns true for an unused/invalid option.
     */
    bool isLast() const
    {
      return isTagged(next_);
    }
  
    /**
     * @brief Returns a pointer to the first element of the linked list.
     *
     * Use this when you want the first occurrence of an option on the command line to
     * take precedence. Note that this is not the way most programs handle options.
     * You should probably be using last() instead.
     *
     * @note
     * This method may be called on an unused/invalid option and will return a pointer to the
     * option itself.
     */
    Option* first()
    {
      Option* p = this;
      while (!p->isFirst())
        p = p->prev_;
      return p;
    }
  
    /**
     * @brief Returns a pointer to the last element of the linked list.
     *
     * Use this when you want the last occurrence of an option on the command line to
     * take precedence. This is the most common way of handling conflicting options.
     *
     * @note
     * This method may be called on an unused/invalid option and will return a pointer to the
     * option itself.
     *
     * @par Tip:
     * If you have options with opposite meanings (e.g. @c --enable-foo and @c --disable-foo), you
     * can assign them the same Descriptor::index to get them into the same list. Distinguish them by
     * Descriptor::type and all you have to do is check <code> last()->type() </code> to get
     * the state listed last on the command line.
     */
    Option* last()
    {
      return first()->prevwrap();
    }
  
    /**
     * @brief Returns a pointer to the previous element of the linked list or NULL if
     * called on first().
     *
     * If called on first() this method returns NULL. Otherwise it will return the
     * option with the same Descriptor::index that precedes this option on the command
     * line.
     */
    Option* prev()
    {
      return isFirst() ? 0 : prev_;
    }
  
    /**
     * @brief Returns a pointer to the previous element of the linked list with wrap-around from
     * first() to last().
     *
     * If called on first() this method returns last(). Otherwise it will return the
     * option with the same Descriptor::index that precedes this option on the command
     * line.
     */
    Option* prevwrap()
    {
      return untag(prev_);
    }
  
    /**
     * @brief Returns a pointer to the next element of the linked list or NULL if called
     * on last().
     *
     * If called on last() this method returns NULL. Otherwise it will return the
     * option with the same Descriptor::index that follows this option on the command
     * line.
     */
    Option* next()
    {
      return isLast() ? 0 : next_;
    }
  
    /**
     * @brief Returns a pointer to the next element of the linked list with wrap-around from
     * last() to first().
     *
     * If called on last() this method returns first(). Otherwise it will return the
     * option with the same Descriptor::index that follows this option on the command
     * line.
     */
    Option* nextwrap()
    {
      return untag(next_);
    }
  
    /**
     * @brief Makes @c new_last the new last() by chaining it into the list after last().
     *
     * It doesn't matter which element you call append() on. The new element will always
     * be appended to last().
     *
     * @attention
     * @c new_last must not yet be part of a list, or that list will become corrupted, because
     * this method does not unchain @c new_last from an existing list.
     */
    void append(Option* new_last)
    {
      Option* p = last();
      Option* f = first();
      p->next_ = new_last;
      new_last->prev_ = p;
      new_last->next_ = tag(f);
      f->prev_ = tag(new_last);
    }
  
    /**
     * @brief Casts from Option to const Option* but only if this Option is valid.
     *
     * If this Option is valid (i.e. @c desc!=NULL), returns this.
     * Otherwise returns NULL. This allows testing an Option directly
     * in an if-clause to see if it is used:
     * @code
     * if (options[CREATE])
     * {
     *   ...
     * }
     * @endcode
     * It also allows you to write loops like this:
     * @code for (Option* opt = options[FILE]; opt; opt = opt->next())
     *   fname = opt->arg; ... @endcode
     */
    operator const Option*() const
    {
      return desc ? this : 0;
    }
  
    /**
     * @brief Casts from Option to Option* but only if this Option is valid.
     *
     * If this Option is valid (i.e. @c desc!=NULL), returns this.
     * Otherwise returns NULL. This allows testing an Option directly
     * in an if-clause to see if it is used:
     * @code
     * if (options[CREATE])
     * {
     *   ...
     * }
     * @endcode
     * It also allows you to write loops like this:
     * @code for (Option* opt = options[FILE]; opt; opt = opt->next())
     *   fname = opt->arg; ... @endcode
     */
    operator Option*()
    {
      return desc ? this : 0;
    }
  
    /**
     * @brief Creates a new Option that is a one-element linked list and has NULL
     * @ref desc, @ref name, @ref arg and @ref namelen.
     */
    Option() :
        desc(0), name(0), arg(0), namelen(0)
    {
      prev_ = tag(this);
      next_ = tag(this);
    }
  
    /**
     * @brief Creates a new Option that is a one-element linked list and has the given
     * values for @ref desc, @ref name and @ref arg.
     *
     * If @c name_ points at a character other than '-' it will be assumed to refer to a
     * short option and @ref namelen will be set to 1. Otherwise the length will extend to
     * the first '=' character or the string's 0-terminator.
     */
    Option(const Descriptor* desc_, const char* name_, const char* arg_)
    {
      init(desc_, name_, arg_);
    }
  
    /**
     * @brief Makes @c *this a copy of @c orig except for the linked list pointers.
     *
     * After this operation @c *this will be a one-element linked list.
     */
    void operator=(const Option& orig)
    {
      init(orig.desc, orig.name, orig.arg);
    }
  
    /**
     * @brief Makes @c *this a copy of @c orig except for the linked list pointers.
     *
     * After this operation @c *this will be a one-element linked list.
     */
    Option(const Option& orig)
    {
      init(orig.desc, orig.name, orig.arg);
    }
  
  private:
    /**
     * @internal
     * @brief Sets the fields of this Option to the given values (extracting @c name if necessary).
     *
     * If @c name_ points at a character other than '-' it will be assumed to refer to a
     * short option and @ref namelen will be set to 1. Otherwise the length will extend to
     * the first '=' character or the string's 0-terminator.
     */
    void init(const Descriptor* desc_, const char* name_, const char* arg_)
    {
      desc = desc_;
      name = name_;
      arg = arg_;
      prev_ = tag(this);
      next_ = tag(this);
      namelen = 0;
      if (name == 0)
        return;
      namelen = 1;
      if (name[0] != '-')
        return;
      while (name[namelen] != 0 && name[namelen] != '=')
        ++namelen;
    }
  
    static Option* tag(Option* ptr)
    {
      return (Option*) ((unsigned long long) ptr | 1);
    }
  
    static Option* untag(Option* ptr)
    {
      return (Option*) ((unsigned long long) ptr & ~1ull);
    }
  
    static bool isTagged(Option* ptr)
    {
      return ((unsigned long long) ptr & 1);
    }
  };
  
  /**
   * @brief Functions for checking the validity of option arguments.
   *
   * @copydetails CheckArg
   *
   * The following example code
   * can serve as starting place for writing your own more complex CheckArg functions:
   * @code
   * struct Arg: public option::Arg
   * {
   *   static void printError(const char* msg1, const option::Option& opt, const char* msg2)
   *   {
   *     fprintf(stderr, "ERROR: %s", msg1);
   *     fwrite(opt.name, opt.namelen, 1, stderr);
   *     fprintf(stderr, "%s", msg2);
   *   }
   *
   *   static option::ArgStatus Unknown(const option::Option& option, bool msg)
   *   {
   *     if (msg) printError("Unknown option '", option, "'\n");
   *     return option::ARG_ILLEGAL;
   *   }
   *
   *   static option::ArgStatus Required(const option::Option& option, bool msg)
   *   {
   *     if (option.arg != 0)
   *       return option::ARG_OK;
   *
   *     if (msg) printError("Option '", option, "' requires an argument\n");
   *     return option::ARG_ILLEGAL;
   *   }
   *
   *   static option::ArgStatus NonEmpty(const option::Option& option, bool msg)
   *   {
   *     if (option.arg != 0 && option.arg[0] != 0)
   *       return option::ARG_OK;
   *
   *     if (msg) printError("Option '", option, "' requires a non-empty argument\n");
   *     return option::ARG_ILLEGAL;
   *   }
   *
   *   static option::ArgStatus Numeric(const option::Option& option, bool msg)
   *   {
   *     char* endptr = 0;
   *     if (option.arg != 0 && strtol(option.arg, &endptr, 10)){};
   *     if (endptr != option.arg && *endptr == 0)
   *       return option::ARG_OK;
   *
   *     if (msg) printError("Option '", option, "' requires a numeric argument\n");
   *     return option::ARG_ILLEGAL;
   *   }
   * };
   * @endcode
   */
  struct Arg
  {
  
  
    //! @brief For options that don't take an argument: Returns ARG_NONE.
    static ArgStatus None(const Option&, bool)
    {
      return ARG_NONE;
    }
  
    //! @brief Returns ARG_OK if the argument is attached and ARG_IGNORE otherwise.
    static ArgStatus Optional(const Option& option, bool)
    {
      if (option.arg && option.name[option.namelen] != 0)
        return ARG_OK;
      else
        return ARG_IGNORE;
    }
  
  
    static ArgStatus Required(const OptionParser::Option& option, bool msg)
    {
      if (option.arg != 0)
        return OptionParser::ARG_OK;
  
      if (msg) {
    	  std::cout << "Option '" << option << "' requires an argument\n";
      }
      return OptionParser::ARG_ILLEGAL;
    }
  };
  
  /**
   * @brief Determines the minimum lengths of the buffer and options arrays used for Parser.
   *
   * Because Parser doesn't use dynamic memory its output arrays have to be pre-allocated.
   * If you don't want to use fixed size arrays (which may turn out too small, causing
   * command line arguments to be dropped), you can use Stats to determine the correct sizes.
   * Stats work cumulative. You can first pass in your default options and then the real
   * options and afterwards the counts will reflect the union.
   */
  struct Stats
  {
    /**
     * @brief Number of elements needed for a @c buffer[] array to be used for
     * @ref Parser::parse() "parsing" the same argument vectors that were fed
     * into this Stats object.
     *
     * @note
     * This number is always 1 greater than the actual number needed, to give
     * you a sentinel element.
     */
    unsigned buffer_max;
  
    /**
     * @brief Number of elements needed for an @c options[] array to be used for
     * @ref Parser::parse() "parsing" the same argument vectors that were fed
     * into this Stats object.
     *
     * @note
     * @li This number is always 1 greater than the actual number needed, to give
     * you a sentinel element.
     * @li This number depends only on the @c usage, not the argument vectors, because
     * the @c options array needs exactly one slot for each possible Descriptor::index.
     */
    unsigned options_max;
  
    /**
     * @brief Creates a Stats object with counts set to 1 (for the sentinel element).
     */
    Stats() :
        buffer_max(1), options_max(1) // 1 more than necessary as sentinel
    {
    }
  
    /**
     * @brief Creates a new Stats object and immediately updates it for the
     * given @c usage and argument vector. You may pass 0 for @c argc and/or @c argv,
     * if you just want to update @ref options_max.
     *
     * @note
     * The calls to Stats methods must match the later calls to Parser methods.
     * See Parser::parse() for the meaning of the arguments.
     */
    Stats(bool gnu, const Descriptor usage[], int argc, const char** argv, int min_abbr_len = 0, //
          bool single_minus_longopt = false) :
        buffer_max(1), options_max(1) // 1 more than necessary as sentinel
    {
      add(gnu, usage, argc, argv, min_abbr_len, single_minus_longopt);
    }
  
    //! @brief Stats(...) with non-const argv.
    Stats(bool gnu, const Descriptor usage[], int argc, char** argv, int min_abbr_len = 0, //
          bool single_minus_longopt = false) :
        buffer_max(1), options_max(1) // 1 more than necessary as sentinel
    {
      add(gnu, usage, argc, (const char**) argv, min_abbr_len, single_minus_longopt);
    }
  
    //! @brief POSIX Stats(...) (gnu==false).
    Stats(const Descriptor usage[], int argc, const char** argv, int min_abbr_len = 0, //
          bool single_minus_longopt = false) :
        buffer_max(1), options_max(1) // 1 more than necessary as sentinel
    {
      add(false, usage, argc, argv, min_abbr_len, single_minus_longopt);
    }
  
    //! @brief POSIX Stats(...) (gnu==false) with non-const argv.
    Stats(const Descriptor usage[], int argc, char** argv, int min_abbr_len = 0, //
          bool single_minus_longopt = false) :
        buffer_max(1), options_max(1) // 1 more than necessary as sentinel
    {
      add(false, usage, argc, (const char**) argv, min_abbr_len, single_minus_longopt);
    }
  
    /**
     * @brief Updates this Stats object for the
     * given @c usage and argument vector. You may pass 0 for @c argc and/or @c argv,
     * if you just want to update @ref options_max.
     *
     * @note
     * The calls to Stats methods must match the later calls to Parser methods.
     * See Parser::parse() for the meaning of the arguments.
     */
    void add(bool gnu, const Descriptor usage[], int argc, const char** argv, int min_abbr_len = 0, //
             bool single_minus_longopt = false);
  
    //! @brief add() with non-const argv.
    void add(bool gnu, const Descriptor usage[], int argc, char** argv, int min_abbr_len = 0, //
             bool single_minus_longopt = false)
    {
      add(gnu, usage, argc, (const char**) argv, min_abbr_len, single_minus_longopt);
    }
  
    //! @brief POSIX add() (gnu==false).
    void add(const Descriptor usage[], int argc, const char** argv, int min_abbr_len = 0, //
             bool single_minus_longopt = false)
    {
      add(false, usage, argc, argv, min_abbr_len, single_minus_longopt);
    }
  
    //! @brief POSIX add() (gnu==false) with non-const argv.
    void add(const Descriptor usage[], int argc, char** argv, int min_abbr_len = 0, //
             bool single_minus_longopt = false)
    {
      add(false, usage, argc, (const char**) argv, min_abbr_len, single_minus_longopt);
    }
  private:
    class CountOptionsAction;
  };
  
  /**
   * @brief Checks argument vectors for validity and parses them into data
   * structures that are easier to work with.
   *
   * @par Example:
   * @code
   * int main(int argc, char* argv[])
   * {
   *   argc-=(argc>0); argv+=(argc>0); // skip program name argv[0] if present
   *   option::Stats  stats(usage, argc, argv);
   *   option::Option options[stats.options_max], buffer[stats.buffer_max];
   *   option::Parser parse(usage, argc, argv, options, buffer);
   *
   *   if (parse.error())
   *     return 1;
   *
   *   if (options[HELP])
   *   ...
   * @endcode
   */
  class Parser
  {
    int op_count; //!< @internal @brief see optionsCount()
    int nonop_count; //!< @internal @brief see nonOptionsCount()
    const char** nonop_args; //!< @internal @brief see nonOptions()
    bool err; //!< @internal @brief see error()
  public:
  
    /**
     * @brief Creates a new Parser.
     */
    Parser() :
        op_count(0), nonop_count(0), nonop_args(0), err(false)
    {
    }
  
    /**
     * @brief Creates a new Parser and immediately parses the given argument vector.
     * @copydetails parse()
     */
    Parser(bool gnu, const Descriptor usage[], int argc, const char** argv, Option options[], Option buffer[],
           int min_abbr_len = 0, bool single_minus_longopt = false, int bufmax = -1) :
        op_count(0), nonop_count(0), nonop_args(0), err(false)
    {
      parse(gnu, usage, argc, argv, options, buffer, min_abbr_len, single_minus_longopt, bufmax);
    }
  
    //! @brief Parser(...) with non-const argv.
    Parser(bool gnu, const Descriptor usage[], int argc, char** argv, Option options[], Option buffer[],
           int min_abbr_len = 0, bool single_minus_longopt = false, int bufmax = -1) :
        op_count(0), nonop_count(0), nonop_args(0), err(false)
    {
      parse(gnu, usage, argc, (const char**) argv, options, buffer, min_abbr_len, single_minus_longopt, bufmax);
    }
  
    //! @brief POSIX Parser(...) (gnu==false).
    Parser(const Descriptor usage[], int argc, const char** argv, Option options[], Option buffer[], int min_abbr_len = 0,
           bool single_minus_longopt = false, int bufmax = -1) :
        op_count(0), nonop_count(0), nonop_args(0), err(false)
    {
      parse(false, usage, argc, argv, options, buffer, min_abbr_len, single_minus_longopt, bufmax);
    }
  
    //! @brief POSIX Parser(...) (gnu==false) with non-const argv.
    Parser(const Descriptor usage[], int argc, char** argv, Option options[], Option buffer[], int min_abbr_len = 0,
           bool single_minus_longopt = false, int bufmax = -1) :
        op_count(0), nonop_count(0), nonop_args(0), err(false)
    {
      parse(false, usage, argc, (const char**) argv, options, buffer, min_abbr_len, single_minus_longopt, bufmax);
    }
  
    /**
     * @brief Parses the given argument vector.
     *
     * @param gnu if true, parse() will not stop at the first non-option argument. Instead it will
     *            reorder arguments so that all non-options are at the end. This is the default behaviour
     *            of GNU getopt() but is not conforming to POSIX. @n
     *            Note, that once the argument vector has been reordered, the @c gnu flag will have
     *            no further effect on this argument vector. So it is enough to pass @c gnu==true when
     *            creating Stats.
     * @param usage Array of Descriptor objects that describe the options to support. The last entry
     *              of this array must have 0 in all fields.
     * @param argc The number of elements from @c argv that are to be parsed. If you pass -1, the number
     *             will be determined automatically. In that case the @c argv list must end with a NULL
     *             pointer.
     * @param argv The arguments to be parsed. If you pass -1 as @c argc the last pointer in the @c argv
     *             list must be NULL to mark the end.
     * @param options Each entry is the first element of a linked list of Options. Each new option
     *                that is parsed will be appended to the list specified by that Option's
     *                Descriptor::index. If an entry is not yet used (i.e. the Option is invalid),
     *                it will be replaced rather than appended to. @n
     *                The minimum length of this array is the greatest Descriptor::index value that
     *                occurs in @c usage @e PLUS ONE.
     * @param buffer Each argument that is successfully parsed (including unknown arguments, if they
     *        have a Descriptor whose CheckArg does not return @ref ARG_ILLEGAL) will be stored in this
     *        array. parse() scans the array for the first invalid entry and begins writing at that
     *        index. You can pass @c bufmax to limit the number of options stored.
     * @param min_abbr_len Passing a value <code> min_abbr_len > 0 </code> enables abbreviated long
     *               options. The parser will match a prefix of a long option as if it was
     *               the full long option (e.g. @c --foob=10 will be interpreted as if it was
     *               @c --foobar=10 ), as long as the prefix has at least @c min_abbr_len characters
     *               (not counting the @c -- ) and is unambiguous.
     *               @n Be careful if combining @c min_abbr_len=1 with @c single_minus_longopt=true
     *               because the ambiguity check does not consider short options and abbreviated
     *               single minus long options will take precedence over short options.
     * @param single_minus_longopt Passing @c true for this option allows long options to begin with
     *               a single minus. The double minus form will still be recognized. Note that
     *               single minus long options take precedence over short options and short option
     *               groups. E.g. @c -file would be interpreted as @c --file and not as
     *               <code> -f -i -l -e </code> (assuming a long option named @c "file" exists).
     * @param bufmax The greatest index in the @c buffer[] array that parse() will write to is
     *               @c bufmax-1. If there are more options, they will be processed (in particular
     *               their CheckArg will be called) but not stored. @n
     *               If you used Stats::buffer_max to dimension this array, you can pass
     *               -1 (or not pass @c bufmax at all) which tells parse() that the buffer is
     *               "large enough".
     * @attention
     * Remember that @c options and @c buffer store Option @e objects, not pointers. Therefore it
     * is not possible for the same object to be in both arrays. For those options that are found in
     * both @c buffer[] and @c options[] the respective objects are independent copies. And only the
     * objects in @c options[] are properly linked via Option::next() and Option::prev().
     * You can iterate over @c buffer[] to
     * process all options in the order they appear in the argument vector, but if you want access to
     * the other Options with the same Descriptor::index, then you @e must access the linked list via
     * @c options[]. You can get the linked list in options from a buffer object via something like
     * @c options[buffer[i].index()].
     */
    void parse(bool gnu, const Descriptor usage[], int argc, const char** argv, Option options[], Option buffer[],
               int min_abbr_len = 0, bool single_minus_longopt = false, int bufmax = -1);
  
    //! @brief parse() with non-const argv.
    void parse(bool gnu, const Descriptor usage[], int argc, char** argv, Option options[], Option buffer[],
               int min_abbr_len = 0, bool single_minus_longopt = false, int bufmax = -1)
    {
      parse(gnu, usage, argc, (const char**) argv, options, buffer, min_abbr_len, single_minus_longopt, bufmax);
    }
  
    //! @brief POSIX parse() (gnu==false).
    void parse(const Descriptor usage[], int argc, const char** argv, Option options[], Option buffer[],
               int min_abbr_len = 0, bool single_minus_longopt = false, int bufmax = -1)
    {
      parse(false, usage, argc, argv, options, buffer, min_abbr_len, single_minus_longopt, bufmax);
    }
  
    //! @brief POSIX parse() (gnu==false) with non-const argv.
    void parse(const Descriptor usage[], int argc, char** argv, Option options[], Option buffer[], int min_abbr_len = 0,
               bool single_minus_longopt = false, int bufmax = -1)
    {
      parse(false, usage, argc, (const char**) argv, options, buffer, min_abbr_len, single_minus_longopt, bufmax);
    }
  
    /**
     * @brief Returns the number of valid Option objects in @c buffer[].
     *
     * @note
     * @li The returned value always reflects the number of Options in the buffer[] array used for
     * the most recent call to parse().
     * @li The count (and the buffer[]) includes unknown options if they are collected
     * (see Descriptor::longopt).
     */
    int optionsCount()
    {
      return op_count;
    }
  
    /**
     * @brief Returns the number of non-option arguments that remained at the end of the
     * most recent parse() that actually encountered non-option arguments.
     *
     * @note
     * A parse() that does not encounter non-option arguments will leave this value
     * as well as nonOptions() undisturbed. This means you can feed the Parser a
     * default argument vector that contains non-option arguments (e.g. a default filename).
     * Then you feed it the actual arguments from the user. If the user has supplied at
     * least one non-option argument, all of the non-option arguments from the default
     * disappear and are replaced by the user's non-option arguments. However, if the
     * user does not supply any non-option arguments the defaults will still be in
     * effect.
     */
    int nonOptionsCount()
    {
      return nonop_count;
    }
  
    /**
     * @brief Returns a pointer to an array of non-option arguments (only valid
     * if <code>nonOptionsCount() >0 </code>).
     *
     * @note
     * @li parse() does not copy arguments, so this pointer points into the actual argument
     * vector as passed to parse().
     * @li As explained at nonOptionsCount() this pointer is only changed by parse() calls
     * that actually encounter non-option arguments. A parse() call that encounters only
     * options, will not change nonOptions().
     */
    const char** nonOptions()
    {
      return nonop_args;
    }
  
    /**
     * @brief Returns <b><code>nonOptions()[i]</code></b> (@e without checking if i is in range!).
     */
    const char* nonOption(int i)
    {
      return nonOptions()[i];
    }
  
    /**
     * @brief Returns @c true if an unrecoverable error occurred while parsing options.
     *
     * An illegal argument to an option (i.e. CheckArg returns @ref ARG_ILLEGAL) is an
     * unrecoverable error that aborts the parse. Unknown options are only an error if
     * their CheckArg function returns @ref ARG_ILLEGAL. Otherwise they are collected.
     * In that case if you want to exit the program if either an illegal argument
     * or an unknown option has been passed, use code like this
     *
     * @code
     * if (parser.error() || options[UNKNOWN])
     *   exit(1);
     * @endcode
     *
     */
    bool error()
    {
      return err;
    }
  
  private:
    friend struct Stats;
    class StoreOptionAction;
    struct Action;
  
    /**
     * @internal
     * @brief This is the core function that does all the parsing.
     * @retval false iff an unrecoverable error occurred.
     */
    static bool workhorse(bool gnu, const Descriptor usage[], int numargs, const char** args, Action& action,
                          bool single_minus_longopt, bool print_errors, int min_abbr_len);
  
    /**
     * @internal
     * @brief Returns true iff @c st1 is a prefix of @c st2 and
     * in case @c st2 is longer than @c st1, then
     * the first additional character is '='.
     *
     * @par Examples:
     * @code
     * streq("foo", "foo=bar") == true
     * streq("foo", "foobar")  == false
     * streq("foo", "foo")     == true
     * streq("foo=bar", "foo") == false
     * @endcode
     */
    static bool streq(const char* st1, const char* st2)
    {
      while (*st1 != 0)
        if (*st1++ != *st2++)
          return false;
      return (*st2 == 0 || *st2 == '=');
    }
  
    /**
     * @internal
     * @brief Like streq() but handles abbreviations.
     *
     * Returns true iff @c st1 and @c st2 have a common
     * prefix with the following properties:
     * @li (if min > 0) its length is at least @c min characters or the same length as @c st1 (whichever is smaller).
     * @li (if min <= 0) its length is the same as that of @c st1
     * @li within @c st2 the character following the common prefix is either '=' or end-of-string.
     *
     * Examples:
     * @code
     * streqabbr("foo", "foo=bar",<anything>) == true
     * streqabbr("foo", "fo=bar" , 2) == true
     * streqabbr("foo", "fo"     , 2) == true
     * streqabbr("foo", "fo"     , 0) == false
     * streqabbr("foo", "f=bar"  , 2) == false
     * streqabbr("foo", "f"      , 2) == false
     * streqabbr("fo" , "foo=bar",<anything>)  == false
     * streqabbr("foo", "foobar" ,<anything>)  == false
     * streqabbr("foo", "fobar"  ,<anything>)  == false
     * streqabbr("foo", "foo"    ,<anything>)  == true
     * @endcode
     */
    static bool streqabbr(const char* st1, const char* st2, long long min)
    {
      const char* st1start = st1;
      while (*st1 != 0 && (*st1 == *st2))
      {
        ++st1;
        ++st2;
      }
  
      return (*st1 == 0 || (min > 0 && (st1 - st1start) >= min)) && (*st2 == 0 || *st2 == '=');
    }
  
    /**
     * @internal
     * @brief Returns true iff character @c ch is contained in the string @c st.
     *
     * Returns @c true for @c ch==0 .
     */
    static bool instr(char ch, const char* st)
    {
      while (*st != 0 && *st != ch)
        ++st;
      return *st == ch;
    }
  
    /**
     * @internal
     * @brief Rotates <code>args[-count],...,args[-1],args[0]</code> to become
     *        <code>args[0],args[-count],...,args[-1]</code>.
     */
    static void shift(const char** args, int count)
    {
      for (int i = 0; i > -count; --i)
      {
        const char* temp = args[i];
        args[i] = args[i - 1];
        args[i - 1] = temp;
      }
    }
  };
  
  /**
   * @internal
   * @brief Interface for actions Parser::workhorse() should perform for each Option it
   * parses.
   */
  struct Parser::Action
  {
    /**
     * @brief Called by Parser::workhorse() for each Option that has been successfully
     * parsed (including unknown
     * options if they have a Descriptor whose Descriptor::check_arg does not return
     * @ref ARG_ILLEGAL.
     *
     * Returns @c false iff a fatal error has occured and the parse should be aborted.
     */
    virtual bool perform(Option&)
    {
      return true;
    }
  
    /**
     * @brief Called by Parser::workhorse() after finishing the parse.
     * @param numargs the number of non-option arguments remaining
     * @param args pointer to the first remaining non-option argument (if numargs > 0).
     *
     * @return
     * @c false iff a fatal error has occurred.
     */
    virtual bool finished(int numargs, const char** args)
    {
      (void) numargs;
      (void) args;
      return true;
    }
  };
  
  /**
   * @internal
   * @brief An Action to pass to Parser::workhorse() that will increment a counter for
   * each parsed Option.
   */
  class Stats::CountOptionsAction: public Parser::Action
  {
    unsigned* buffer_max;
  public:
    /**
     * Creates a new CountOptionsAction that will increase @c *buffer_max_ for each
     * parsed Option.
     */
    CountOptionsAction(unsigned* buffer_max_) :
        buffer_max(buffer_max_)
    {
    }
  
    bool perform(Option&)
    {
      if (*buffer_max == 0x7fffffff)
        return false; // overflow protection: don't accept number of options that doesn't fit signed int
      ++*buffer_max;
      return true;
    }
  };
  
  /**
   * @internal
   * @brief An Action to pass to Parser::workhorse() that will store each parsed Option in
   * appropriate arrays (see Parser::parse()).
   */
  class Parser::StoreOptionAction: public Parser::Action
  {
    Parser& parser;
    Option* options;
    Option* buffer;
    int bufmax; //! Number of slots in @c buffer. @c -1 means "large enough".
  public:
    /**
     * @brief Creates a new StoreOption action.
     * @param parser_ the parser whose op_count should be updated.
     * @param options_ each Option @c o is chained into the linked list @c options_[o.desc->index]
     * @param buffer_ each Option is appended to this array as long as there's a free slot.
     * @param bufmax_ number of slots in @c buffer_. @c -1 means "large enough".
     */
    StoreOptionAction(Parser& parser_, Option options_[], Option buffer_[], int bufmax_) :
        parser(parser_), options(options_), buffer(buffer_), bufmax(bufmax_)
    {
      // find first empty slot in buffer (if any)
      int bufidx = 0;
      while ((bufmax < 0 || bufidx < bufmax) && buffer[bufidx])
        ++bufidx;
  
      // set parser's optionCount
      parser.op_count = bufidx;
    }
  
    bool perform(Option& option)
    {
      if (bufmax < 0 || parser.op_count < bufmax)
      {
        if (parser.op_count == 0x7fffffff)
          return false; // overflow protection: don't accept number of options that doesn't fit signed int
  
        buffer[parser.op_count] = option;
        int idx = buffer[parser.op_count].desc->index;
        if (options[idx])
          options[idx].append(buffer[parser.op_count]);
        else
          options[idx] = buffer[parser.op_count];
        ++parser.op_count;
      }
      return true; // NOTE: an option that is discarded because of a full buffer is not fatal
    }
  
    bool finished(int numargs, const char** args)
    {
      // only overwrite non-option argument list if there's at least 1
      // new non-option argument. Otherwise we keep the old list. This
      // makes it easy to use default non-option arguments.
      if (numargs > 0)
      {
        parser.nonop_count = numargs;
        parser.nonop_args = args;
      }
  
      return true;
    }
  };
  
  inline void Parser::parse(bool gnu, const Descriptor usage[], int argc, const char** argv, Option options[],
                            Option buffer[], int min_abbr_len, bool single_minus_longopt, int bufmax)
  {
    StoreOptionAction action(*this, options, buffer, bufmax);
    err = !workhorse(gnu, usage, argc, argv, action, single_minus_longopt, true, min_abbr_len);
  }
  
  inline void Stats::add(bool gnu, const Descriptor usage[], int argc, const char** argv, int min_abbr_len,
                         bool single_minus_longopt)
  {
    // determine size of options array. This is the greatest index used in the usage + 1
    int i = 0;
    while (usage[i].shortopt != 0)
    {
      if (usage[i].index + 1 >= options_max)
        options_max = (usage[i].index + 1) + 1; // 1 more than necessary as sentinel
  
      ++i;
    }
  
    CountOptionsAction action(&buffer_max);
    Parser::workhorse(gnu, usage, argc, argv, action, single_minus_longopt, false, min_abbr_len);
  }
  
  inline bool Parser::workhorse(bool gnu, const Descriptor usage[], int numargs, const char** args, Action& action,
                                bool single_minus_longopt, bool print_errors, int min_abbr_len)
  {
    // protect against NULL pointer
    if (args == 0)
      numargs = 0;
  
    int nonops = 0;
  
    while (numargs != 0 && *args != 0)
    {
      const char* param = *args; // param can be --long-option, -srto or non-option argument
  
      // in POSIX mode the first non-option argument terminates the option list
      // a lone minus character is a non-option argument
      if (param[0] != '-' || param[1] == 0)
      {
        if (gnu)
        {
          ++nonops;
          ++args;
          if (numargs > 0)
            --numargs;
          continue;
        }
        else
          break;
      }
  
      // -- terminates the option list. The -- itself is skipped.
      if (param[1] == '-' && param[2] == 0)
      {
        shift(args, nonops);
        ++args;
        if (numargs > 0)
          --numargs;
        break;
      }
  
      bool handle_short_options;
      const char* longopt_name;
      if (param[1] == '-') // if --long-option
      {
        handle_short_options = false;
        longopt_name = param + 2;
      }
      else
      {
        handle_short_options = true;
        longopt_name = param + 1; //for testing a potential -long-option
      }
  
      bool try_single_minus_longopt = single_minus_longopt;
      bool have_more_args = (numargs > 1 || numargs < 0); // is referencing argv[1] valid?
  
      do // loop over short options in group, for long options the body is executed only once
      {
        int idx;
  
        const char* optarg;
  
        /******************** long option **********************/
        if (handle_short_options == false || try_single_minus_longopt)
        {
          idx = 0;
          while (usage[idx].longopt != 0 && !streq(usage[idx].longopt, longopt_name))
            ++idx;
  
          if (usage[idx].longopt == 0 && min_abbr_len > 0) // if we should try to match abbreviated long options
          {
            int i1 = 0;
            while (usage[i1].longopt != 0 && !streqabbr(usage[i1].longopt, longopt_name, min_abbr_len))
              ++i1;
            if (usage[i1].longopt != 0)
            { // now test if the match is unambiguous by checking for another match
              int i2 = i1 + 1;
              while (usage[i2].longopt != 0 && !streqabbr(usage[i2].longopt, longopt_name, min_abbr_len))
                ++i2;
  
              if (usage[i2].longopt == 0) // if there was no second match it's unambiguous, so accept i1 as idx
                idx = i1;
            }
          }
  
          // if we found something, disable handle_short_options (only relevant if single_minus_longopt)
          if (usage[idx].longopt != 0)
            handle_short_options = false;
  
          try_single_minus_longopt = false; // prevent looking for longopt in the middle of shortopt group
  
          optarg = longopt_name;
          while (*optarg != 0 && *optarg != '=')
            ++optarg;
          if (*optarg == '=') // attached argument
            ++optarg;
          else
            // possibly detached argument
            optarg = (have_more_args ? args[1] : 0);
        }
  
        /************************ short option ***********************************/
        if (handle_short_options)
        {
          if (*++param == 0) // point at the 1st/next option character
            break; // end of short option group
  
          idx = 0;
          while (usage[idx].shortopt != 0 && !instr(*param, usage[idx].shortopt))
            ++idx;
  
          if (param[1] == 0) // if the potential argument is separate
            optarg = (have_more_args ? args[1] : 0);
          else
            // if the potential argument is attached
            optarg = param + 1;
        }
  
        const Descriptor* descriptor = &usage[idx];
  
        if (descriptor->shortopt == 0) /**************  unknown option ********************/
        {
          // look for dummy entry (shortopt == "" and longopt == "") to use as Descriptor for unknown options
          idx = 0;
          while (usage[idx].shortopt != 0 && (usage[idx].shortopt[0] != 0 || usage[idx].longopt[0] != 0))
            ++idx;
          descriptor = (usage[idx].shortopt == 0 ? 0 : &usage[idx]);
        }
  
        if (descriptor != 0)
        {
          Option option(descriptor, param, optarg);
          switch (descriptor->check_arg(option, print_errors))
          {
            case ARG_ILLEGAL:
              return false; // fatal
            case ARG_OK:
              // skip one element of the argument vector, if it's a separated argument
              if (optarg != 0 && have_more_args && optarg == args[1])
              {
                shift(args, nonops);
                if (numargs > 0)
                  --numargs;
                ++args;
              }
  
              // No further short options are possible after an argument
              handle_short_options = false;
  
              break;
            case ARG_IGNORE:
            case ARG_NONE:
              option.arg = 0;
              break;
          }
  
          if (!action.perform(option))
            return false;
        }
  
      } while (handle_short_options);
  
      shift(args, nonops);
      ++args;
      if (numargs > 0)
        --numargs;
  
    } // while
  
    if (numargs > 0 && *args == 0) // It's a bug in the caller if numargs is greater than the actual number
      numargs = 0; // of arguments, but as a service to the user we fix this if we spot it.
  
    if (numargs < 0) // if we don't know the number of remaining non-option arguments
    { // we need to count them
      numargs = 0;
      while (args[numargs] != 0)
        ++numargs;
    }
  
    return action.finished(numargs + nonops, args - nonops);
  }
  
  /**
   * @internal
   * @brief The implementation of option::printUsage().
   */
  struct PrintUsageImplementation
  {
    /**
     * @internal
     * @brief Interface for Functors that write (part of) a string somewhere.
     */
    struct IStringWriter
    {
      /**
       * @brief Writes the given number of chars beginning at the given pointer somewhere.
       */
      virtual void operator()(const char*, int)
      {
      }
    };
  
    /**
     * @internal
     * @brief Encapsulates a function with signature <code>func(string, size)</code> where
     * string can be initialized with a const char* and size with an int.
     */
    template<typename Function>
    struct FunctionWriter: public IStringWriter
    {
      Function* write;
  
      virtual void operator()(const char* str, int size)
      {
        (*write)(str, size);
      }
  
      FunctionWriter(Function* w) :
          write(w)
      {
      }
    };
  
    /**
     * @internal
     * @brief Encapsulates a reference to an object with a <code>write(string, size)</code>
     * method like that of @c std::ostream.
     */
    template<typename OStream>
    struct OStreamWriter: public IStringWriter
    {
      OStream& ostream;
  
      virtual void operator()(const char* str, int size)
      {
        ostream.write(str, size);
      }
  
      OStreamWriter(OStream& o) :
          ostream(o)
      {
      }
    };
  
    /**
     * @internal
     * @brief Like OStreamWriter but encapsulates a @c const reference, which is
     * typically a temporary object of a user class.
     */
    template<typename Temporary>
    struct TemporaryWriter: public IStringWriter
    {
      const Temporary& userstream;
  
      virtual void operator()(const char* str, int size)
      {
        userstream.write(str, size);
      }
  
      TemporaryWriter(const Temporary& u) :
          userstream(u)
      {
      }
    };
  
    /**
     * @internal
     * @brief Encapsulates a function with the signature <code>func(fd, string, size)</code> (the
     * signature of the @c write() system call)
     * where fd can be initialized from an int, string from a const char* and size from an int.
     */
    template<typename Syscall>
    struct SyscallWriter: public IStringWriter
    {
      Syscall* write;
      int fd;
  
      virtual void operator()(const char* str, int size)
      {
        (*write)(fd, str, size);
      }
  
      SyscallWriter(Syscall* w, int f) :
          write(w), fd(f)
      {
      }
    };
  
    /**
     * @internal
     * @brief Encapsulates a function with the same signature as @c std::fwrite().
     */
    template<typename Function, typename Stream>
    struct StreamWriter: public IStringWriter
    {
      Function* fwrite;
      Stream* stream;
  
      virtual void operator()(const char* str, int size)
      {
        (*fwrite)(str, size, 1, stream);
      }
  
      StreamWriter(Function* w, Stream* s) :
          fwrite(w), stream(s)
      {
      }
    };
  
    /**
     * @internal
     * @brief Sets <code> i1 = max(i1, i2) </code>
     */
    static void upmax(int& i1, int i2)
    {
      i1 = (i1 >= i2 ? i1 : i2);
    }
  
    /**
     * @internal
     * @brief Moves the "cursor" to column @c want_x assuming it is currently at column @c x
     * and sets @c x=want_x .
     * If <code> x > want_x </code>, a line break is output before indenting.
     *
     * @param write Spaces and possibly a line break are written via this functor to get
     *        the desired indentation @c want_x .
     * @param[in,out] x the current indentation. Set to @c want_x by this method.
     * @param want_x the desired indentation.
     */
    static void indent(IStringWriter& write, int& x, int want_x)
    {
      int indent = want_x - x;
      if (indent < 0)
      {
        write("\n", 1);
        indent = want_x;
      }
  
      if (indent > 0)
      {
        char space = ' ';
        for (int i = 0; i < indent; ++i)
          write(&space, 1);
        x = want_x;
      }
    }
  
    /**
     * @brief Returns true if ch is the unicode code point of a wide character.
     *
     * @note
     * The following character ranges are treated as wide
     * @code
     * 1100..115F
     * 2329..232A  (just 2 characters!)
     * 2E80..A4C6  except for 303F
     * A960..A97C
     * AC00..D7FB
     * F900..FAFF
     * FE10..FE6B
     * FF01..FF60
     * FFE0..FFE6
     * 1B000......
     * @endcode
     */
    static bool isWideChar(unsigned ch)
    {
      if (ch == 0x303F)
        return false;
  
      return ((0x1100 <= ch && ch <= 0x115F) || (0x2329 <= ch && ch <= 0x232A) || (0x2E80 <= ch && ch <= 0xA4C6)
          || (0xA960 <= ch && ch <= 0xA97C) || (0xAC00 <= ch && ch <= 0xD7FB) || (0xF900 <= ch && ch <= 0xFAFF)
          || (0xFE10 <= ch && ch <= 0xFE6B) || (0xFF01 <= ch && ch <= 0xFF60) || (0xFFE0 <= ch && ch <= 0xFFE6)
          || (0x1B000 <= ch));
    }
  
    /**
     * @internal
     * @brief Splits a @c Descriptor[] array into tables, rows, lines and columns and
     * iterates over these components.
     *
     * The top-level organizational unit is the @e table.
     * A table begins at a Descriptor with @c help!=NULL and extends up to
     * a Descriptor with @c help==NULL.
     *
     * A table consists of @e rows. Due to line-wrapping and explicit breaks
     * a row may take multiple lines on screen. Rows within the table are separated
     * by \\n. They never cross Descriptor boundaries. This means a row ends either
     * at \\n or the 0 at the end of the help string.
     *
     * A row consists of columns/cells. Columns/cells within a row are separated by \\t.
     * Line breaks within a cell are marked by \\v.
     *
     * Rows in the same table need not have the same number of columns/cells. The
     * extreme case are interjections, which are rows that contain neither \\t nor \\v.
     * These are NOT treated specially by LinePartIterator, but they are treated
     * specially by printUsage().
     *
     * LinePartIterator iterates through the usage at 3 levels: table, row and part.
     * Tables and rows are as described above. A @e part is a line within a cell.
     * LinePartIterator iterates through 1st parts of all cells, then through the 2nd
     * parts of all cells (if any),... @n
     * Example: The row <code> "1 \v 3 \t 2 \v 4" </code> has 2 cells/columns and 4 parts.
     * The parts will be returned in the order 1, 2, 3, 4.
     *
     * It is possible that some cells have fewer parts than others. In this case
     * LinePartIterator will "fill up" these cells with 0-length parts. IOW, LinePartIterator
     * always returns the same number of parts for each column. Note that this is different
     * from the way rows and columns are handled. LinePartIterator does @e not guarantee that
     * the same number of columns will be returned for each row.
     *
     */
    class LinePartIterator
    {
      const Descriptor* tablestart; //!< The 1st descriptor of the current table.
      const Descriptor* rowdesc; //!< The Descriptor that contains the current row.
      const char* rowstart; //!< Ptr to 1st character of current row within rowdesc->help.
      const char* ptr; //!< Ptr to current part within the current row.
      int col; //!< Index of current column.
      int len; //!< Length of the current part (that ptr points at) in BYTES
      int screenlen; //!< Length of the current part in screen columns (taking narrow/wide chars into account).
      int max_line_in_block; //!< Greatest index of a line within the block. This is the number of \\v within the cell with the most \\vs.
      int line_in_block; //!< Line index within the current cell of the current part.
      int target_line_in_block; //!< Line index of the parts we should return to the user on this iteration.
      bool hit_target_line; //!< Flag whether we encountered a part with line index target_line_in_block in the current cell.
  
      /** 
       * @brief Determines the byte and character lengths of the part at @ref ptr and 
       * stores them in @ref len and @ref screenlen respectively.
       */
      void update_length()
      {
        screenlen = 0;
        for (len = 0; ptr[len] != 0 && ptr[len] != '\v' && ptr[len] != '\t' && ptr[len] != '\n'; ++len)
        {
          ++screenlen;
          unsigned ch = (unsigned char) ptr[len];
          if (ch > 0xC1) // everything <= 0xC1 (yes, even 0xC1 itself) is not a valid UTF-8 start byte
          {
            // int __builtin_clz (unsigned int x)
            // Returns the number of leading 0-bits in x, starting at the most significant bit
            unsigned mask = (unsigned) -1 >> __builtin_clz(ch ^ 0xff);
            ch = ch & mask; // mask out length bits, we don't verify their correctness
            while (((unsigned char) ptr[len + 1] ^ 0x80) <= 0x3F) // while next byte is continuation byte
            {
              ch = (ch << 6) ^ (unsigned char) ptr[len + 1] ^ 0x80; // add continuation to char code
              ++len;
            }
            // ch is the decoded unicode code point
            if (ch >= 0x1100 && isWideChar(ch)) // the test for 0x1100 is here to avoid the function call in the Latin case
              ++screenlen;
          }
        }
      }
  
    public:
      //! @brief Creates an iterator for @c usage.
      LinePartIterator(const Descriptor usage[]) :
          tablestart(usage), rowdesc(0), rowstart(0), ptr(0), col(-1), len(0), max_line_in_block(0), line_in_block(0),
          target_line_in_block(0), hit_target_line(true)
      {
      }
  
      /**
       * @brief Moves iteration to the next table (if any). Has to be called once on a new
       * LinePartIterator to move to the 1st table.
       * @retval false if moving to next table failed because no further table exists.
       */
      bool nextTable()
      {
        // If this is NOT the first time nextTable() is called after the constructor,
        // then skip to the next table break (i.e. a Descriptor with help == 0)
        if (rowdesc != 0)
        {
          while (tablestart->help != 0 && tablestart->shortopt != 0)
            ++tablestart;
        }
  
        // Find the next table after the break (if any)
        while (tablestart->help == 0 && tablestart->shortopt != 0)
          ++tablestart;
  
        restartTable();
        return rowstart != 0;
      }
  
      /**
       * @brief Reset iteration to the beginning of the current table.
       */
      void restartTable()
      {
        rowdesc = tablestart;
        rowstart = tablestart->help;
        ptr = 0;
      }
  
      /**
       * @brief Moves iteration to the next row (if any). Has to be called once after each call to
       * @ref nextTable() to move to the 1st row of the table.
       * @retval false if moving to next row failed because no further row exists.
       */
      bool nextRow()
      {
        if (ptr == 0)
        {
          restartRow();
          return rowstart != 0;
        }
  
        while (*ptr != 0 && *ptr != '\n')
          ++ptr;
  
        if (*ptr == 0)
        {
          if ((rowdesc + 1)->help == 0) // table break
            return false;
  
          ++rowdesc;
          rowstart = rowdesc->help;
        }
        else // if (*ptr == '\n')
        {
          rowstart = ptr + 1;
        }
  
        restartRow();
        return true;
      }
  
      /**
       * @brief Reset iteration to the beginning of the current row.
       */
      void restartRow()
      {
        ptr = rowstart;
        col = -1;
        len = 0;
        screenlen = 0;
        max_line_in_block = 0;
        line_in_block = 0;
        target_line_in_block = 0;
        hit_target_line = true;
      }
  
      /**
       * @brief Moves iteration to the next part (if any). Has to be called once after each call to
       * @ref nextRow() to move to the 1st part of the row.
       * @retval false if moving to next part failed because no further part exists.
       *
       * See @ref LinePartIterator for details about the iteration.
       */
      bool next()
      {
        if (ptr == 0)
          return false;
  
        if (col == -1)
        {
          col = 0;
          update_length();
          return true;
        }
  
        ptr += len;
        while (true)
        {
          switch (*ptr)
          {
            case '\v':
              upmax(max_line_in_block, ++line_in_block);
              ++ptr;
              break;
            case '\t':
              if (!hit_target_line) // if previous column did not have the targetline
              { // then "insert" a 0-length part
                update_length();
                hit_target_line = true;
                return true;
              }
  
              hit_target_line = false;
              line_in_block = 0;
              ++col;
              ++ptr;
              break;
            case 0:
            case '\n':
              if (!hit_target_line) // if previous column did not have the targetline
              { // then "insert" a 0-length part
                update_length();
                hit_target_line = true;
                return true;
              }
  
              if (++target_line_in_block > max_line_in_block)
              {
                update_length();
                return false;
              }
  
              hit_target_line = false;
              line_in_block = 0;
              col = 0;
              ptr = rowstart;
              continue;
            default:
              ++ptr;
              continue;
          } // switch
  
          if (line_in_block == target_line_in_block)
          {
            update_length();
            hit_target_line = true;
            return true;
          }
        } // while
      }
  
      /**
       * @brief Returns the index (counting from 0) of the column in which
       * the part pointed to by @ref data() is located.
       */
      int column()
      {
        return col;
      }
  
      /**
       * @brief Returns the index (counting from 0) of the line within the current column
       * this part belongs to.
       */
      int line()
      {
        return target_line_in_block; // NOT line_in_block !!! It would be wrong if !hit_target_line
      }
  
      /**
       * @brief Returns the length of the part pointed to by @ref data() in raw chars (not UTF-8 characters).
       */
      int length()
      {
        return len;
      }
  
      /**
       * @brief Returns the width in screen columns of the part pointed to by @ref data().
       * Takes multi-byte UTF-8 sequences and wide characters into account.
       */
      int screenLength()
      {
        return screenlen;
      }
  
      /**
       * @brief Returns the current part of the iteration.
       */
      const char* data()
      {
        return ptr;
      }
    };
  
    /**
     * @internal
     * @brief Takes input and line wraps it, writing out one line at a time so that
     * it can be interleaved with output from other columns.
     *
     * The LineWrapper is used to handle the last column of each table as well as interjections.
     * The LineWrapper is called once for each line of output. If the data given to it fits
     * into the designated width of the last column it is simply written out. If there
     * is too much data, an appropriate split point is located and only the data up to this
     * split point is written out. The rest of the data is queued for the next line.
     * That way the last column can be line wrapped and interleaved with data from
     * other columns. The following example makes this clearer:
     * @code
     * Column 1,1    Column 2,1     This is a long text
     * Column 1,2    Column 2,2     that does not fit into
     *                              a single line.
     * @endcode
     *
     * The difficulty in producing this output is that the whole string
     * "This is a long text that does not fit into a single line" is the
     * 1st and only part of column 3. In order to produce the above
     * output the string must be output piecemeal, interleaved with
     * the data from the other columns.
     */
    class LineWrapper
    {
      static const int bufmask = 15; //!< Must be a power of 2 minus 1.
      /**
       * @brief Ring buffer for length component of pair (data, length).
       */
      int lenbuf[bufmask + 1];
      /**
       * @brief Ring buffer for data component of pair (data, length).
       */
      const char* datbuf[bufmask + 1];
      /**
       * @brief The indentation of the column to which the LineBuffer outputs. LineBuffer
       * assumes that the indentation has already been written when @ref process()
       * is called, so this value is only used when a buffer flush requires writing
       * additional lines of output.
       */
      int x;
      /**
       * @brief The width of the column to line wrap.
       */
      int width;
      int head; //!< @brief index for next write
      int tail; //!< @brief index for next read - 1 (i.e. increment tail BEFORE read)
  
      /**
       * @brief Multiple methods of LineWrapper may decide to flush part of the buffer to
       * free up space. The contract of process() says that only 1 line is output. So
       * this variable is used to track whether something has output a line. It is
       * reset at the beginning of process() and checked at the end to decide if
       * output has already occurred or is still needed.
       */
      bool wrote_something;
  
      bool buf_empty()
      {
        return ((tail + 1) & bufmask) == head;
      }
  
      bool buf_full()
      {
        return tail == head;
      }
  
      void buf_store(const char* data, int len)
      {
        lenbuf[head] = len;
        datbuf[head] = data;
        head = (head + 1) & bufmask;
      }
  
      //! @brief Call BEFORE reading ...buf[tail].
      void buf_next()
      {
        tail = (tail + 1) & bufmask;
      }
  
      /**
       * @brief Writes (data,len) into the ring buffer. If the buffer is full, a single line
       * is flushed out of the buffer into @c write.
       */
      void output(IStringWriter& write, const char* data, int len)
      {
        if (buf_full())
          write_one_line(write);
  
        buf_store(data, len);
      }
  
      /**
       * @brief Writes a single line of output from the buffer to @c write.
       */
      void write_one_line(IStringWriter& write)
      {
        if (wrote_something) // if we already wrote something, we need to start a new line
        {
          write("\n", 1);
          int _ = 0;
          indent(write, _, x);
        }
  
        if (!buf_empty())
        {
          buf_next();
          write(datbuf[tail], lenbuf[tail]);
        }
  
        wrote_something = true;
      }
    public:
  
      /**
       * @brief Writes out all remaining data from the LineWrapper using @c write.
       * Unlike @ref process() this method indents all lines including the first and
       * will output a \\n at the end (but only if something has been written).
       */
      void flush(IStringWriter& write)
      {
        if (buf_empty())
          return;
        int _ = 0;
        indent(write, _, x);
        wrote_something = false;
        while (!buf_empty())
          write_one_line(write);
        write("\n", 1);
      }
  
      /**
       * @brief Process, wrap and output the next piece of data.
       *
       * process() will output at least one line of output. This is not necessarily
       * the @c data passed in. It may be data queued from a prior call to process().
       * If the internal buffer is full, more than 1 line will be output.
       *
       * process() assumes that the a proper amount of indentation has already been
       * output. It won't write any further indentation before the 1st line. If
       * more than 1 line is written due to buffer constraints, the lines following
       * the first will be indented by this method, though.
       *
       * No \\n is written by this method after the last line that is written.
       *
       * @param write where to write the data.
       * @param data the new chunk of data to write.
       * @param len the length of the chunk of data to write.
       */
      void process(IStringWriter& write, const char* data, int len)
      {
        wrote_something = false;
  
        while (len > 0)
        {
          if (len <= width) // quick test that works because utf8width <= len (all wide chars have at least 2 bytes)
          {
            output(write, data, len);
            len = 0;
          }
          else // if (len > width)  it's possible (but not guaranteed) that utf8len > width
          {
            int utf8width = 0;
            int maxi = 0;
            while (maxi < len && utf8width < width)
            {
              int charbytes = 1;
              unsigned ch = (unsigned char) data[maxi];
              if (ch > 0xC1) // everything <= 0xC1 (yes, even 0xC1 itself) is not a valid UTF-8 start byte
              {
                // int __builtin_clz (unsigned int x)
                // Returns the number of leading 0-bits in x, starting at the most significant bit
                unsigned mask = (unsigned) -1 >> __builtin_clz(ch ^ 0xff);
                ch = ch & mask; // mask out length bits, we don't verify their correctness
                while ((maxi + charbytes < len) && //
                    (((unsigned char) data[maxi + charbytes] ^ 0x80) <= 0x3F)) // while next byte is continuation byte
                {
                  ch = (ch << 6) ^ (unsigned char) data[maxi + charbytes] ^ 0x80; // add continuation to char code
                  ++charbytes;
                }
                // ch is the decoded unicode code point
                if (ch >= 0x1100 && isWideChar(ch)) // the test for 0x1100 is here to avoid the function call in the Latin case
                {
                  if (utf8width + 2 > width)
                    break;
                  ++utf8width;
                }
              }
              ++utf8width;
              maxi += charbytes;
            }
  
            // data[maxi-1] is the last byte of the UTF-8 sequence of the last character that fits
            // onto the 1st line. If maxi == len, all characters fit on the line.
  
            if (maxi == len)
            {
              output(write, data, len);
              len = 0;
            }
            else // if (maxi < len)  at least 1 character (data[maxi] that is) doesn't fit on the line
            {
              int i;
              for (i = maxi; i >= 0; --i)
                if (data[i] == ' ')
                  break;
  
              if (i >= 0)
              {
                output(write, data, i);
                data += i + 1;
                len -= i + 1;
              }
              else // did not find a space to split at => split before data[maxi]
              { // data[maxi] is always the beginning of a character, never a continuation byte
                output(write, data, maxi);
                data += maxi;
                len -= maxi;
              }
            }
          }
        }
        if (!wrote_something) // if we didn't already write something to make space in the buffer
          write_one_line(write); // write at most one line of actual output
      }
  
      /**
       * @brief Constructs a LineWrapper that wraps its output to fit into
       * screen columns @c x1 (incl.) to @c x2 (excl.).
       *
       * @c x1 gives the indentation LineWrapper uses if it needs to indent.
       */
      LineWrapper(int x1, int x2) :
          x(x1), width(x2 - x1), head(0), tail(bufmask)
      {
        if (width < 2) // because of wide characters we need at least width 2 or the code breaks
          width = 2;
      }
    };
  
    /**
     * @internal
     * @brief This is the implementation that is shared between all printUsage() templates.
     * Because all printUsage() templates share this implementation, there is no template bloat.
     */
    static void printUsage(IStringWriter& write, const Descriptor usage[], int width = 80, //
                           int last_column_min_percent = 50, int last_column_own_line_max_percent = 75)
    {
      if (width < 1) // protect against nonsense values
        width = 80;
  
      if (width > 10000) // protect against overflow in the following computation
        width = 10000;
  
      int last_column_min_width = ((width * last_column_min_percent) + 50) / 100;
      int last_column_own_line_max_width = ((width * last_column_own_line_max_percent) + 50) / 100;
      if (last_column_own_line_max_width == 0)
        last_column_own_line_max_width = 1;
  
      LinePartIterator part(usage);
      while (part.nextTable())
      {
  
        /***************** Determine column widths *******************************/
  
        const int maxcolumns = 8; // 8 columns are enough for everyone
        int col_width[maxcolumns];
        int lastcolumn;
        int leftwidth;
        int overlong_column_threshold = 10000;
        do
        {
          lastcolumn = 0;
          for (int i = 0; i < maxcolumns; ++i)
            col_width[i] = 0;
  
          part.restartTable();
          while (part.nextRow())
          {
            while (part.next())
            {
              if (part.column() < maxcolumns)
              {
                upmax(lastcolumn, part.column());
                if (part.screenLength() < overlong_column_threshold)
                  // We don't let rows that don't use table separators (\t or \v) influence
                  // the width of column 0. This allows the user to interject section headers
                  // or explanatory paragraphs that do not participate in the table layout.
                  if (part.column() > 0 || part.line() > 0 || part.data()[part.length()] == '\t'
                      || part.data()[part.length()] == '\v')
                    upmax(col_width[part.column()], part.screenLength());
              }
            }
          }
  
          /*
           * If the last column doesn't fit on the same
           * line as the other columns, we can fix that by starting it on its own line.
           * However we can't do this for any of the columns 0..lastcolumn-1.
           * If their sum exceeds the maximum width we try to fix this by iteratively
           * ignoring the widest line parts in the width determination until
           * we arrive at a series of column widths that fit into one line.
           * The result is a layout where everything is nicely formatted
           * except for a few overlong fragments.
           * */
  
          leftwidth = 0;
          overlong_column_threshold = 0;
          for (int i = 0; i < lastcolumn; ++i)
          {
            leftwidth += col_width[i];
            upmax(overlong_column_threshold, col_width[i]);
          }
  
        } while (leftwidth > width);
  
        /**************** Determine tab stops and last column handling **********************/
  
        int tabstop[maxcolumns];
        tabstop[0] = 0;
        for (int i = 1; i < maxcolumns; ++i)
          tabstop[i] = tabstop[i - 1] + col_width[i - 1];
  
        int rightwidth = width - tabstop[lastcolumn];
        bool print_last_column_on_own_line = false;
        if (rightwidth < last_column_min_width && rightwidth < col_width[lastcolumn])
        {
          print_last_column_on_own_line = true;
          rightwidth = last_column_own_line_max_width;
        }
  
        // If lastcolumn == 0 we must disable print_last_column_on_own_line because
        // otherwise 2 copies of the last (and only) column would be output.
        // Actually this is just defensive programming. It is currently not
        // possible that lastcolumn==0 and print_last_column_on_own_line==true
        // at the same time, because lastcolumn==0 => tabstop[lastcolumn] == 0 =>
        // rightwidth==width => rightwidth>=last_column_min_width  (unless someone passes
        // a bullshit value >100 for last_column_min_percent) => the above if condition
        // is false => print_last_column_on_own_line==false
        if (lastcolumn == 0)
          print_last_column_on_own_line = false;
  
        LineWrapper lastColumnLineWrapper(width - rightwidth, width);
        LineWrapper interjectionLineWrapper(0, width);
  
        part.restartTable();
  
        /***************** Print out all rows of the table *************************************/
  
        while (part.nextRow())
        {
          int x = -1;
          while (part.next())
          {
            if (part.column() > lastcolumn)
              continue; // drop excess columns (can happen if lastcolumn == maxcolumns-1)
  
            if (part.column() == 0)
            {
              if (x >= 0)
                write("\n", 1);
              x = 0;
            }
  
            indent(write, x, tabstop[part.column()]);
  
            if ((part.column() < lastcolumn)
                && (part.column() > 0 || part.line() > 0 || part.data()[part.length()] == '\t'
                    || part.data()[part.length()] == '\v'))
            {
              write(part.data(), part.length());
              x += part.screenLength();
            }
            else // either part.column() == lastcolumn or we are in the special case of
                 // an interjection that doesn't contain \v or \t
            {
              // NOTE: This code block is not necessarily executed for
              // each line, because some rows may have fewer columns.
  
              LineWrapper& lineWrapper = (part.column() == 0) ? interjectionLineWrapper : lastColumnLineWrapper;
  
              if (!print_last_column_on_own_line)
                lineWrapper.process(write, part.data(), part.length());
            }
          } // while
  
          if (print_last_column_on_own_line)
          {
            part.restartRow();
            while (part.next())
            {
              if (part.column() == lastcolumn)
              {
                write("\n", 1);
                int _ = 0;
                indent(write, _, width - rightwidth);
                lastColumnLineWrapper.process(write, part.data(), part.length());
              }
            }
          }
  
          write("\n", 1);
          lastColumnLineWrapper.flush(write);
          interjectionLineWrapper.flush(write);
        }
      }
    }
  
  }
  ;
  
  /**
   * @brief Outputs a nicely formatted usage string with support for multi-column formatting
   * and line-wrapping.
   *
   * printUsage() takes the @c help texts of a Descriptor[] array and formats them into
   * a usage message, wrapping lines to achieve the desired output width.
   *
   * <b>Table formatting:</b>
   *
   * Aside from plain strings which are simply line-wrapped, the usage may contain tables. Tables
   * are used to align elements in the output.
   *
   * @code
   * // Without a table. The explanatory texts are not aligned.
   * -c, --create  |Creates something.
   * -k, --kill  |Destroys something.
   *
   * // With table formatting. The explanatory texts are aligned.
   * -c, --create  |Creates something.
   * -k, --kill    |Destroys something.
   * @endcode
   *
   * Table formatting removes the need to pad help texts manually with spaces to achieve
   * alignment. To create a table, simply insert \\t (tab) characters to separate the cells
   * within a row.
   *
   * @code
   * const option::Descriptor usage[] = {
   * {..., "-c, --create  \tCreates something." },
   * {..., "-k, --kill  \tDestroys something." }, ...
   * @endcode
   *
   * Note that you must include the minimum amount of space desired between cells yourself.
   * Table formatting will insert further spaces as needed to achieve alignment.
   *
   * You can insert line breaks within cells by using \\v (vertical tab).
   *
   * @code
   * const option::Descriptor usage[] = {
   * {..., "-c,\v--create  \tCreates\vsomething." },
   * {..., "-k,\v--kill  \tDestroys\vsomething." }, ...
   *
   * // results in
   *
   * -c,       Creates
   * --create  something.
   * -k,       Destroys
   * --kill    something.
   * @endcode
   *
   * You can mix lines that do not use \\t or \\v with those that do. The plain
   * lines will not mess up the table layout. Alignment of the table columns will
   * be maintained even across these interjections.
   *
   * @code
   * const option::Descriptor usage[] = {
   * {..., "-c, --create  \tCreates something." },
   * {..., "----------------------------------" },
   * {..., "-k, --kill  \tDestroys something." }, ...
   *
   * // results in
   *
   * -c, --create  Creates something.
   * ----------------------------------
   * -k, --kill    Destroys something.
   * @endcode
   *
   * You can have multiple tables within the same usage whose columns are
   * aligned independently. Simply insert a dummy Descriptor with @c help==0.
   *
   * @code
   * const option::Descriptor usage[] = {
   * {..., "Long options:" },
   * {..., "--very-long-option  \tDoes something long." },
   * {..., "--ultra-super-mega-long-option  \tTakes forever to complete." },
   * {..., 0 }, // ---------- table break -----------
   * {..., "Short options:" },
   * {..., "-s  \tShort." },
   * {..., "-q  \tQuick." }, ...
   *
   * // results in
   *
   * Long options:
   * --very-long-option              Does something long.
   * --ultra-super-mega-long-option  Takes forever to complete.
   * Short options:
   * -s  Short.
   * -q  Quick.
   *
   * // Without the table break it would be
   *
   * Long options:
   * --very-long-option              Does something long.
   * --ultra-super-mega-long-option  Takes forever to complete.
   * Short options:
   * -s                              Short.
   * -q                              Quick.
   * @endcode
   *
   * <b>Output methods:</b>
   *
   * Because TheLeanMeanC++Option parser is freestanding, you have to provide the means for
   * output in the first argument(s) to printUsage(). Because printUsage() is implemented as
   * a set of template functions, you have great flexibility in your choice of output
   * method. The following example demonstrates typical uses. Anything that's similar enough
   * will work.
   *
   * @code
   * #include <unistd.h>  // write()
   * #include <iostream>  // cout
   * #include <sstream>   // ostringstream
   * #include <cstdio>    // fwrite()
   * using namespace std;
   *
   * void my_write(const char* str, int size) {
   *   fwrite(str, size, 1, stdout);
   * }
   *
   * struct MyWriter {
   *   void write(const char* buf, size_t size) const {
   *      fwrite(str, size, 1, stdout);
   *   }
   * };
   *
   * struct MyWriteFunctor {
   *   void operator()(const char* buf, size_t size) {
   *      fwrite(str, size, 1, stdout);
   *   }
   * };
   * ...
   * printUsage(my_write, usage);    // custom write function
   * printUsage(MyWriter(), usage);  // temporary of a custom class
   * MyWriter writer;
   * printUsage(writer, usage);      // custom class object
   * MyWriteFunctor wfunctor;
   * printUsage(&wfunctor, usage);   // custom functor
   * printUsage(write, 1, usage);    // write() to file descriptor 1
   * printUsage(cout, usage);        // an ostream&
   * printUsage(fwrite, stdout, usage);  // fwrite() to stdout
   * ostringstream sstr;
   * printUsage(sstr, usage);        // an ostringstream&
   *
   * @endcode
   *
   * @par Notes:
   * @li the @c write() method of a class that is to be passed as a temporary
   *     as @c MyWriter() is in the example, must be a @c const method, because
   *     temporary objects are passed as const reference. This only applies to
   *     temporary objects that are created and destroyed in the same statement.
   *     If you create an object like @c writer in the example, this restriction
   *     does not apply.
   * @li a functor like @c MyWriteFunctor in the example must be passed as a pointer.
   *     This differs from the way functors are passed to e.g. the STL algorithms.
   * @li All printUsage() templates are tiny wrappers around a shared non-template implementation.
   *     So there's no penalty for using different versions in the same program.
   * @li printUsage() always interprets Descriptor::help as UTF-8 and always produces UTF-8-encoded
   *     output. If your system uses a different charset, you must do your own conversion. You
   *     may also need to change the font of the console to see non-ASCII characters properly.
   *     This is particularly true for Windows.
   * @li @b Security @b warning: Do not insert untrusted strings (such as user-supplied arguments)
   *     into the usage. printUsage() has no protection against malicious UTF-8 sequences.
   *
   * @param prn The output method to use. See the examples above.
   * @param usage the Descriptor[] array whose @c help texts will be formatted.
   * @param width the maximum number of characters per output line. Note that this number is
   *        in actual characters, not bytes. printUsage() supports UTF-8 in @c help and will
   *        count multi-byte UTF-8 sequences properly. Asian wide characters are counted
   *        as 2 characters.
   * @param last_column_min_percent (0-100) The minimum percentage of @c width that should be available
   *        for the last column (which typically contains the textual explanation of an option).
   *        If less space is available, the last column will be printed on its own line, indented
   *        according to @c last_column_own_line_max_percent.
   * @param last_column_own_line_max_percent (0-100) If the last column is printed on its own line due to
   *        less than @c last_column_min_percent of the width being available, then only
   *        @c last_column_own_line_max_percent of the extra line(s) will be used for the
   *        last column's text. This ensures an indentation. See example below.
   *
   * @code
   * // width=20, last_column_min_percent=50 (i.e. last col. min. width=10)
   * --3456789 1234567890
   *           1234567890
   *
   * // width=20, last_column_min_percent=75 (i.e. last col. min. width=15)
   * // last_column_own_line_max_percent=75
   * --3456789
   *      123456789012345
   *      67890
   *
   * // width=20, last_column_min_percent=75 (i.e. last col. min. width=15)
   * // last_column_own_line_max_percent=33 (i.e. max. 5)
   * --3456789
   *                12345
   *                67890
   *                12345
   *                67890
   * @endcode
   */
  template<typename OStream>
  void printUsage(OStream& prn, const Descriptor usage[], int width = 80, int last_column_min_percent = 50,
                  int last_column_own_line_max_percent = 75)
  {
    PrintUsageImplementation::OStreamWriter<OStream> write(prn);
    PrintUsageImplementation::printUsage(write, usage, width, last_column_min_percent, last_column_own_line_max_percent);
  }
  
  template<typename Function>
  void printUsage(Function* prn, const Descriptor usage[], int width = 80, int last_column_min_percent = 50,
                  int last_column_own_line_max_percent = 75)
  {
    PrintUsageImplementation::FunctionWriter<Function> write(prn);
    PrintUsageImplementation::printUsage(write, usage, width, last_column_min_percent, last_column_own_line_max_percent);
  }
  
  template<typename Temporary>
  void printUsage(const Temporary& prn, const Descriptor usage[], int width = 80, int last_column_min_percent = 50,
                  int last_column_own_line_max_percent = 75)
  {
    PrintUsageImplementation::TemporaryWriter<Temporary> write(prn);
    PrintUsageImplementation::printUsage(write, usage, width, last_column_min_percent, last_column_own_line_max_percent);
  }
  
  template<typename Syscall>
  void printUsage(Syscall* prn, int fd, const Descriptor usage[], int width = 80, int last_column_min_percent = 50,
                  int last_column_own_line_max_percent = 75)
  {
    PrintUsageImplementation::SyscallWriter<Syscall> write(prn, fd);
    PrintUsageImplementation::printUsage(write, usage, width, last_column_min_percent, last_column_own_line_max_percent);
  }
  
  template<typename Function, typename Stream>
  void printUsage(Function* prn, Stream* stream, const Descriptor usage[], int width = 80, int last_column_min_percent =
                      50,
                  int last_column_own_line_max_percent = 75)
  {
    PrintUsageImplementation::StreamWriter<Function, Stream> write(prn, stream);
    PrintUsageImplementation::printUsage(write, usage, width, last_column_min_percent, last_column_own_line_max_percent);
  }
  
  }
  // namespace option
  
  #endif /* OPTIONPARSER_H_ */
  